Protective means for electric furnaces



A ril 15 1924. 1,490,408

T. VAN ALLER PROTECTIVE MEANS FOR ELECTRIC FURNACES Filed April 26, 1922 InVentorI Tycho Van Alien y (2W 2 fi H is WCCO rn ey Patented Apr. 15, 1924. I

' UNITED STATES TYCEO vaN arms,

1,490,408 PATENT OFFICE.

or SCHENECTADY, ew Yon'x, A'ssIe on r GENERAL ELECTRIC COMPANY, a CORPORATION or NEW YORK,

rao'rnc'rrvn MEANS I roa nmsc'rmc FURNACES.

Application flledApril as, 1922. Serial no. 556,782.

To all whom it may concern: g

, Be it known that I, TYCHO VAN'ALLER, a citizen of the United States, residing at Schenectady, in .the county of Schenectady, State of New York,'have invented certain new and useful Improvements in Protective .'Means for Electric Furnaces, of which the followingis a specification.

My invention relates to protective means for electric furnaces and has for its object the provision of means for opening the heating circuit of the furnace. upon the occurrence of a predetermined maximum temperature therin.

.More specifically my invention relates to high temperature electric furnaces such as are used, for example, in theheat treatment of metals for the purpose of annealing, hardening, etc. Such, furnaces are commonly heated by a resistance heater which is designed -to safely withstand a certain maximum temperature. This maximum safe temperature is often only slightly higher than the maximum working tem rature (approximately 900 C.) required in the furnace, and conse uentlypare must be taken in the operation 0 sucha furnace, particularly 1 when operating at the maximum working temperature, to prevent overheating and destruction of the heatingelement. Such overheating may also result in damage to the furnace walls and the charge being heated. It is therefore imperative in prolonging the useful life of the furnace that some means be provided to protect furnaces of any other cause. I have found that afuse made of silver provides a simple, reliable and efficient means for protecting furnaces I preferably mount the where it is exposed to the temperature of the furnace and arrange the element so that it will open the heating circuit of the furnace when subjected to a temperature sufli cient to fuse it. I have found that silver, while ossessing the property of resisting oxidation essential in a fuse, has also the characteristic of fusing at a temperature making it suitable for the protection of high tem rature electric furnaces, particularly hig temperature resistance fumac'es- Where a somewhat higher maximum safe temperature is either permissible or desirable, gold lends itself as a suitable fuse metal. a

- For a better understandin of'my invention, reference should be he to the accompanying drawing in which .Fi 1 1s a perspective View of a fuse embo ying my invention; Fig. 2 is a view of the fusible element and leads before the insulating beads are ap lied; while Fig. 3 is a diagrammatic view s owing an electric furnace equipped with a protective means embodying my invention.

Rcferrin to the drawing, the fuse 10 in one form 0 my invention comprises a short strip or link 11 of silver, forming a fusible element, which is electrically connected at its ends to two short heat refractor electrically conducting leads 12and 13. he leads may be formed, for example, of nickel chromium alloy resistance material. The fusible element 11 may be welded or otherwise connected to the leads after which insulating beads 14 are slipped on the leads and fusible element and the fusible element bent inter- 'mediate its ends to form the whole in the shape of a hair pin, the heads 12 and 13 being substantially parallel and insulated by beads '14. One of the beads 14' is positioned on the fusible element across the end of the a eyelets 15 and 16 whereby the fuse may be conveniently connected in an electric circuit. This also secures the beads in place on the leads. c

As shown in Fig. 3, the fuse is mounted in the high temperature resistance furnace 17 with the leads 12 and 13 extending through the wall 18, and the fusible element 11 with the bead 14' located in' the interior of the furnace so as to be exposed to the temperature therein. The fuse may beconvnected, as shown in the drawing, 1n circuit with the operating coil 19 of a contact or switch 20 which e resistance heater 2f of the furnace to a suitable source of supply 22. Operating coil 19 is also energized from supply source 22. When the o crating coil isenergized the contactor is eld in closed position and the resistance heater 21' thus connected to the su ply source 22. I

n 'a-high temperature furnace of the resistance type the maximpm possible safe temperature is limited by t eheat refractory ects the connection of the characteristics of the resistance heating element. With the usual heating resistance material, for example, nickel I chromium alloy, this maximum temperature is, ap roximately from 1000 to 1100 degrees A temperature of 800 to 900 degrees C. has been found to be ample for the heat treatment of metals, such as in annealing, hardening, etc. This, however, leaves asmall margin between the maximum working temperature required and the maximum safe working temperature of the furnace. As a protective device to prevent overheatin in the furnace silver, by reason of its melting point at 961 degrees C. is therefore particularly adapted.

The fusible element may be heated somewhat by the passage through it of the exciting current for the operating coil 19 and consequently may fuse upon the occurrence of a furnace temperature somewhat lower than the melting point of silver. "Under normal conditions of operation the operating coil circuit will be maintained closed through the fuse 10. Upon the occurrence of a temperature in the furnace approaching its maximum safe temperature the fusible element will melt opening the circuit of operating coil 19, whereupon the contactor will drop out disconnecting the resistance heater. The opening of the control circuit is made more positive and excessive arcing prevented by the bead 14; which immediately falls upon the fus ng of the element 11.

By using the heat r iractory leads 12 and 13 the amount of the usible metal necessary may be limited to only that portion of the fuse which is exposed directly to the temperature of the furnace, whereby the cost of the fuse, is greatly reduced. The conductors 12 and 13 extend through the furnace walls and serve as a means for connecting the fusible element in a suitable electric circuit.

In case a somewhat higher maximum temperature limit is desired the fusible element may be made of gold.

\Vhile I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patent statutes, it should be understood that I do not limit my invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departin from the spirit of my invention, the scopeo which is set forth in the annexed claims.

What claim as new and desire to secure by Letters Patent of the United States, is i 1. The combination with a high temperature electric furnace, of a fuse of non-oxidizable metal subjected to the temperature in said furnace and adapted to control the heating circuit of said furnace upon the occurrence of a predetermined temperature therein.

2. The combination with a high temperature electric resistance furnace, of a fuse of silver subjected to the temperature in the furnace and adapted to control the,heating circuit of said furnace upon the occurrence of a predetermined temperature therein.

3. A protective device for electric furnaces comprising insulated heat refractory electrical conductors extending through the wall of said furnace, and a link of non-oxiclizable fusible metal in said furnace connecting the inner ends of said conductors and adapted to open a circuit therethrough to control the heating circuit of said furnace upon the occurrence of a predetermined temperature therein.

4. A protective device for electric furnaces comprising insulated heat refractory electrical conductors extending through the wall of said furnace, and a link of silver in said furnace connectin the inner ends of said conductors and adapted to control a circuit therethrough to open the heating circuit of said furnace upon the occurrence. of

a predetermined temperature therein.

In witness whereof, I have hereunto set my hand this 25th day of April, 1922.

TYCHO VAN ALLER. 

